1. Field of the Invention
The present invention relates to a laminate printed board in which two printed boards are laminated and connected by a plurality of interboard terminals, and a manufacturing method thereof
2. Description of Related Art
Conventionally, a laminate printed board in which two printed boards are laminated and mutually connected by a plurality of interboard terminals, such as that described in Japanese Patent Laid-open Publication No. 2009-26464 (Related Art 1), for example, has been used as an internal circuit in an electrical connection box, such as a junction box mounted in an automobile.
In this type of laminate printed board, first ends of a plurality of interboard terminals are inserted through and soldered to one set of respective through-holes on a first printed board. Also, second ends are inserted through and soldered to another set of respective through-holes on a second printed board. Thus, should the plurality of interboard terminals not be accurately positioned at the stage of soldering to the first printed board, there is a risk that insertion through the through-holes of the second printed board will become difficult.
Supporting the plurality of interboard terminals with a synthetic resin base has been suggested in the laminate printed board described in Related Art 1. However, such a configuration leads to an increase in the number of components due to the necessity of a base as a separate component. In addition, there is a risk that the base may thermally expand from heat of soldering or the like, pulling on the interboard terminals and producing positional drift. Good alignment accuracy thus cannot necessarily be ensured and cracks may occur in the soldering portions of the interboard terminals.
In addition, soldering the interboard terminals to the two printed boards requires the first ends of the interboard terminals first be in a state inserted through the through-holes of the first printed board, immersing the bottom surface of the printed board in a soldering pot to be flow soldered, then inserting the second ends through the through-holes of the second printed board to form an assembly, and inverting the assembly to immerse in the soldering pot the bottom surface of the second printed board, on which the second ends project, to be flow soldered once more. The process had been cumbersome and required time and effort. In particular, in a case where the electronic components mounted on the printed board are of a surface-mounted type only, a flow soldering process must be performed to solder only the interboard terminals, separate from the reflow soldering process for the surface-mounted components, and there is a risk that this may lead to a decrease in manufacturing efficiency.